From automotive technology, functions and methods are known for opening and closing a friction clutch during driving, in order to carry out shifting operations. One of the essential quality objectives of these clutch operations is to carry out transmission gearshifts with the least possible residual torque in the drive-train. Namely, opening of the clutch when there is residual torque leads to a subjectively worse perception and to oscillations in the drive-train, which have a negative influence on a subsequent shift. In principle it is sought to gain separation of the drive-train in a condition of zero torque transmission. One way of doing this is to influence the motor torque, and another is by appropriate control of the clutch. In this, the aim is to keep any torque impulse in the drive-train as small as possible by virtue of a well-judged overlap of the two processes.
This overlapping control of the motor torque and the opening of the friction clutch is relatively difficult to master, because the process depends essentially on two influencing factors which can be determined only imprecisely by evaluating the sensor signals in the vehicle, on the one hand the current frictional properties of the friction clutch, which are dependent inter alia on the temperature, and on the other hand the residual torque still present in the drive-train. A further problem is that the displacement control of the friction clutch is relatively sluggish.
Above all, on uphill gradients the time window until a thrust torque is produced following a traction torque in the drive-train, is relatively short. Consequently, very severe demands are made on the control of a friction clutch and on the friction clutch itself.
In the present application a through-connection clutch is understood to be a clutch which is designed as a friction clutch during a slipping phase, whereas in phases when slipping of the clutch is not desired, the motor torque is transmitted by an interlocked connection between the motor and the transmission. Such a clutch, for example, is disclosed by WO 2006/110945 A1.
Through-connection clutches have a great advantage in that the frictional portion of the clutch only has to be designed for the torque needed for starting processes, but not for the maximum motor torque plus the usual safety factors, since the torque transmission during normal driving operation takes place by positive interlock.
During driving, for the purpose of carrying out shifting operations such clutches, like conventional clutches, can be opened and closed by virtue of the frictional portion of the clutch. The interlock connection is not engaged until the synchronization process between the rotational speeds of the motor and the transmission input shaft after a shift by means of the frictional part of the clutch has been completed.